Generally, in the IEEE802.16e system of which internal standardization for broadband wireless access system is in progress, more efficient data transmission is enabled using a plurality of frequency allocations (FAs). Namely, unlike the conventional method of transmitting data within a band by allocating one frequency band to one base station, several frequency bands are allocated to one base station to increase subscriber accommodation and to transmit data more efficiently.
FIG. 1 is a diagram of inter-frequency handover within one cell and inter-frequency handover between different cells in a broadband wireless access system supporting multiple FAs.
Referring to FIG. 1, in a multiple FA system, if a mobile subscriber station receives data using a first frequency band FA1 within one cell, it may be attempted to receive data that need a wider bandwidth such as multimedia data. In this case, if a resource of the first frequency band FA1 is already occupied by another mobile subscriber station, it is impossible to offer a multimedia service to the corresponding mobile subscriber station via the first frequency band FA1. So, the multimedia service may be enabled in a manner of allocating a second frequency band FA2 which is still reserved to the corresponding mobile subscriber station.
For this, an inter-FA handover is needed. The inter-FA handover, as shown in FIG. 1, can be performed in two ways. Namely, a first case is that a handover 11 is carried out within one cell from the first frequency band FA1 to the second frequency band FA2. And, a second case is that a handover 12 is carried out from a first frequency band FA1 to a fourth frequency band FA4 in a cell using the first frequency band FA1.
However, in case of using the multiple FA, it is necessary to perform the inter-FA handover within one cell or between different cells. Yet, an inter-FA handover method has not been proposed yet in case of using the multiple FA within one cell.
Besides, in case that a mobile subscriber station performs handover from a serving base station to a handover target base station, it has not been decided yet that the handover is performed in which way of the multiple FA provided by the handover target base station. And, how to perform the handover in such a case has not been proposed yet.